After cell entry, the RNA genome of retroviruses is converted to a cDNA copy by reverse transcriptase (RT). For productive infection, the resulting viral cDNA must be integrated into the host chromosome, a process catalyzed by integrase (IN). Certain mutations of HIV-1 IN appear to specifically impair reverse transcription with no apparent effects on other steps in the life cycle. However, the underlying mechanism for this defect is poorly understood. In vitro, RT and IN physically interact, but the biological relevance of this RT- IN interaction is not known. We hypothesize that the physical interaction between RT and IN is functional and critical for initiating reverse transcription during HIV-1 replication. Using nuclear magnetic resonance spectroscopy, we have identified the RT-interacting surface on IN, and have determined the affinity and kinetics of RT-IN complex formation by using a surface plasmon resonance-based biosensor. The goals of this application are to gain a better understanding of the physical interaction between HIV-1 RT and IN, and to determine the functional significance of the RT-IN interaction during HIV-1 replication. The specific aims are (1) to characterize the physical interaction between HIV-1 IN and RT and confirm that the interaction between RT and IN occurs in vivo, and (2) to determine the biological significance of the HIV-1 RT-IN interaction. In Aim 1, we will map the IN-interacting domain of RT using a targeted protein footprinting method. The physical interaction between RT and IN during replication will be confirmed by carrying out a co-immunoprecipitation experiment using purified virions and cytoplasmic extracts from infected cells. In Aim 2, we will test the biological relevance of the RT-IN interaction during infection by disrupting the putative IN-RT binding interface and assessing viral replication. We will also screen for RT mutants that can compensate for the RT- noninteracting IN mutations and examine other IN mutants known to produce defects in reverse transcription for their ability to bind RT. Finally, we will identify small-molecule inhibitors of the RT-IN interaction using a fluorescence-based high-throughput screen and determine whether such inhibitors also block viral replication. In the process, we will shed light on the interaction between two key retroviral enzymes and the effect of such an interaction on reverse transcription and viral replication. Characterization of the RT-IN interaction and determination of its biological significance may reveal new functional roles for IN, provide a mechanistic basis for the phenotypes observed with certain IN mutants, and identify new potential targets for anti-HIV therapy. PUBLIC HEALTH RELEVANCE: The objective of this proposal is to understand the importance of the physical interaction between two key enzymes, reverse transcriptase and integrase, of human immunodeficiency virus type I (HIV-1). Characterization of the interaction and determination of its biological significance may reveal new functional roles for integrase and provide a deeper understanding of the basic biology of the virus. Furthermore, the study may identify new potential targets for anti-HIV therapy.